1. Field of the Invention
The present invention relates to a color cathode ray tube, and more particularly, to a panel and a shadow mask in a color cathode ray tube having a curvature and a radius of curvature required for displaying a picture.
2. Background of the Related Art
In general, the cathode ray tube is a major component for displaying the picture in displays, such as TV receiver, or a computer monitor. FIG. 1 illustrates a side view with a partial cut away view of the color cathode ray tube.
Referring to FIG. 1, there is a fluorescent film 1a having red, green, and blue fluorescent materials on an inside surface of a panel 1, a funnel 2 at rear of the panel 1 welded thereto with Frit glass, and an electron gun 4 in a neck portion 2a of the funnel. There is a shadow mask 5 fitted to the frame 6 for selecting colors of the electron beams 3 from the electron gun 4. The frame 6 is inserted in stud pins 1b fixed to sidewalls of the panel 1 by means of supporting springs 8 fixed to the frame 6, hanging from the sidewalls of the panel 1. There is an inner shield 7 fitted to one side of the frame 6 for protecting the electron beams 3 traveling toward the fluorescent film 1a from external geomagnetism. There is a deflection yoke 10 having a plurality of poles fitted to an outer circumference of the neck portion 2a for correcting a path of travel of the electron beams 3 to hit onto a required fluorescent material accurately, and a reinforcing band 9 strapped around the cathode ray tube for preventing the cathode ray tube suffering from damage by an external impact. Within a basic structure of the cathode ray tube, the panel 1 and the shadow mask 5 form an assembly having a required geometrical relation to each other. That is, the shadow mask 5 is formed to have a curvature required with respect to a curvature of the panel 1, and fitted to have a gap required with respect to the panel 1, so that the three electron beams from the electron gun 4 hit onto the fluorescent material on the inside surface of the panel 1 through the shadow mask 5 to reproduce a picture. Therefore, in order to reproduce a high quality picture, an accurate design of the shadow mask 6 is required, taking an inside surface curvature of the panel 1 into account at first as a condition of the design. FIG. 2 illustrates a section of a panel assembly, referring to which a relation between the inside surface curvature of the panel and the curvature of the shadow mask will be explained.
Referring to FIG. 2, the panel 1 has curved inside and curved outside surfaces, wherein a radius Rop of curvature of the outside curved surface of the panel 1 and a radius Rip of curvature of the inside curved surface of the panel 1 are formed to have a Rop greater than Rip relation so that the panel 1 can withstand a vacuum inside of the cathode ray tube. As radiuses Rop and Rip of the curvatures are inversely proportional to the curvatures, the curvature of the inside curved surface of the panel 1 is greater than the curvature of the outside curved surface of the panel 1. Since geometrical characteristics of the panel 1 and the shadow mask 5 are required to be the same for displaying the picture in fact, the curvature of the inside surface of the panel 1 is taken into account as an element that fixes the curvature of the shadow mask 5, which curvature of the shadow mask 5 has close relation with a structural strength and thermal deformation characteristic of the shadow mask 5. That is, the greater the curvature of the shadow mask 5, the more the structural strength and the thermal deformation characteristic improved.
In addition to the relation between the curvatures and the radiuses of the curvatures, as shown in FIG. 2, there are an arc curvature shown in a solid line and a super arc curvature shown in a dashed line in forms of the curvatures applicable to the inside surface of the panel 1 and the shadow mask 5. The arc curvature is one a portion of a sphere is applied thereto, and the super arc curvature is one in which a curvature becomes the greater as it goes the farther to outside. These forms of curvatures are applicable to the inside surface of the panel 1 selectively, according to which the shadow mask 5 also has either the arc curvature or the super arc curvature. As shown in FIG. 2, since the super arc curvature has height variation of the shadow mask 5 relatively smaller than the arc curvature, the super arc curvature is favorable to thermal deformation. Though the arc curvature and the super arc curvature have been applied to the panel 1 and the shadow mask 5 without particular preference, the super arc curvature is used widely when the thermal deformation is taken into account. Moreover, since curvatures of, not only the panel 1, but also the shadow mask 5, are designed large adequately in view of structural strength, no particular attention is paid thereto. However, recently panel 1 has the radius Rop of curvature of outside surface fully planar or greater than 40,000 mm close to a perfect plane for improving a picture quality, according to which the radius Rip of curvature of inside surface of the panel 1, dependent on the radius Rop of curvature of outside surface of the panel 1, is also increased, and the radius of curvature of the shadow mask 5, dependent on the radius Rip of curvature of the inside surface, is also increased. In other words, according to the inversely proportional relationship between the curvature and the radius of curvature, the curvature of inside surface of the panel 1 and the curvature of the shadow mask 5 are reduced, respectively.
As explained, the reduced curvature of the shadow mask 5 makes the structural strength and thermal deformation of the shadow mask 5 poor. Particularly, the poor structural strength causes howling, shaking of picture by impact or speaker sound, and defective color reproducibility, a variation of picture color, as well as deformation of the shadow mask 5 by external impact or load. Currently, since the problem of thermal deformation is resolved by means of, not the curvature of the shadow mask 5 or similar to this, but reflecting the thermal electron at a reflective film (not shown) coated on a surface of collision of the electron beams 3, a method for improving the structural strength of the shadow mask 5 is required.
Accordingly, the present invention is directed to a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a color cathode ray tube having a shadow mask of improved structural strength.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the color cathode ray tube includes a panel having a substantially flat outside surface and an inside surface with a curvature, and a shadow mask at rear of the panel formed to have a curvature, wherein, when Rxp denotes a radius of curvature of the inside surface of the panel in a long axis direction, Ryp denotes a radius of curvature of the inside surface of the panel in a short axis direction, Rdm denotes a radius of curvature of the shadow mask in a diagonal axis direction, and xe2x80x98Wxe2x80x99 denotes a ratio of a thickness of an end portion of an effective surface of the panel to a thickness of a center portion of the panel, the radius Rxp of curvature of the inside surface of the panel in the long axis direction, and the radius Ryp of curvature of the inside surface of the panel in the short axis direction can be respectively expressed as follows;
Rxp=(Axc2x7W+B)xc2x7Rdm(A=xe2x88x920.217, 1.607 less than B less than 2.446)
Ryp=(Cxc2x7W+D)xc2x7Rdm(C=xe2x88x920.074, 0.799 less than D less than 1.227).
When Rdp denotes the radius of curvature of the inside surface of the panel in the diagonal axis direction, the Rdp can be expressed as follows,       R    dp    =                    (                              4            ·                          R              xp                                +                      3            ·                          R              yp                                      )                    (                              E            ·            W                    +          F                )              ⁢                  (                              E            =            0.011                    ,                      xe2x80x83                    ⁢                      F            =            6.655                          )            .      
It is preferable that the ratio of a thickness of an end portion of an effective surface of the panel to a thickness of a center portion of the panel xe2x80x98Wxe2x80x99 falls within a range of 1.4 less than W less than 2.5.
When Ldme denotes a distance from a center of the shadow mask to an end of the effective surface of the shadow mask in the diagonal axis direction, and Hdme denotes a height at the end of the shadow mask in the diagonal axis direction, the radius of curvature Rdm of the shadow mask in the diagonal axis direction can be expressed as follows.       R    dm    =                              L          dme          2                +                  H          dme          2                            2        ⁢                  H          dme                      .  
When Xm denotes a coordinate on the long axis of the shadow mask, Ym denotes a coordinate on the short axis of the shadow mask, and Zm denotes a coordinate on a height axis of the shadow mask, the curvature of the shadow mask can be expressed as follows.
Zm=Rdmxe2x88x92{square root over (Rdm2xe2x88x92(Xm2+Ym2))}.
When xe2x80x98xcex1xe2x80x99 denotes a dispersion come from a fabrication process and a deflection yoke, a curvature structure of the shadow mask can be expressed as follows, taking the dispersion into account.             Z      m        =                  R        dm            -                                                  R              dm              2                        -                          (                                                X                  m                  2                                +                                  Y                  m                  2                                            )                                      ±        α              ,      
    ⁢                    where,              ⁢      α        =                                                                      X                m                2                            +                              Y                m                2                                              xc3x97                      (                                          L                dme                            -                                                                    X                    m                    2                                    +                                      Y                    m                    2                                                                        )                                    44.456          ⁢                      L            dme                              .      
The curvature structure of the present invention substantially enhances a structural strength of the shadow mask, which prevents deterioration of a color reproducibility caused by vibration and deformation of the shadow mask caused by an external impact.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.